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Continuous glucose monitoring

Continuous glucose monitoring can help you manage your glucose levels in real-time and relieve the burden of having to do multiple finger prick tests throughout the day. Because they are continuous, they also measure your glucose overnight.
Content last reviewed and updated: 13.03.2024

A woman sitting in a park, wearing a continuous glucose monitor

What is a continuous glucose monitor?

A continuous glucose monitor, or CGM, is a small wearable device that measures your glucose levels in real-time. It uses a sensor to continuously send information to a handset or compatible mobile phone so that you can see what your current levels are and whether they’re heading up or down. You can also set alarms to signal if your glucose levels are going too high or too low and see your glucose trends over time.

How does a continuous glucose monitor work?

You attach a CGM directly onto the skin, usually on the upper arm or stomach. A short wire from a sensor goes under the skin and senses how much glucose there is in the fluid between your blood vessels and cells (this is called interstitial fluid).

A transmitter then beams this information to a receiver, which might be a handset, your compatible mobile phone or compatible insulin pump.

You wear the sensor for six to 14 days (depending on the make of the CGM) and then replace it with a new one.

CGMs can be used however you take your insulin, whether you are using multiple daily injections (MDI) or an insulin pump.

What are the benefits of continuous glucose monitoring?

Checking trends

One of the main benefits of CGM is that it allows you to get a wider picture of your glucose levels. When you use a blood glucose meter, you only see what your glucose levels are at the time that you take the measurement. With CGM, you can see your current level, where it’s heading, and review the data over the last few hours or days. This means that you get a fuller picture of what is happening to your levels throughout the day and night, for example, when you’re exercising, eating or sleeping.

Alarms for hypos and hypers

A CGM alerts you if your glucose levels are heading low or high. This allows you to take action so you can minimise or avoid hypos or hypers before they happen. CGMs can help improve your time in range, which is very important when you’re managing type 1 diabetes.

Sharing data

CGM allows you to easily share your glucose data with your loved ones, carers or healthcare team, in real-time or for long-term review. If you’re a parent or guardian of a child with type 1, this means you can see their glucose levels remotely or alert the school if your child is having a hypo. Sharing it with your diabetes team means they can look at the data and see your glucose trends over time, as well as looking at your Hba1c.

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Are there downsides to continuous glucose monitoring?

Using a CGM can take time to get used to, but the downsides are minimal.

Because a CGM doesn’t measure the amount of glucose in the blood itself, you may also need to do a finger prick measurement to calibrate the system or confirm the reading is accurate before acting on it, for example treating a hyper. This can depend on the type of CGM you’re using, so always check with the manufacturer or your Diabetes Healthcare Team.

Some people experience something called alarm fatigue, when you feel annoyed or overwhelmed by the number of alerts from your CGM. Your Diabetes Healthcare Team can help you set the best levels for your alerts, so you don’t keep being alerted about something if you’re not planning to take any action. For example, you may decide not to correct high glucose levels until it reaches a particular number.

What is the difference between continuous and flash glucose monitoring?

Flash glucose monitoring is when you use the Freestyle Libre 2 sensor with the dedicated handset. When you want to get a reading you scan – or ‘flash’ – the sensor. When you use the Freestyle Libre sensor with the app on your phone, it gives continuous real-time readings, which makes it a CGM.

What other technology can a continuous glucose monitor work with?

Hybrid closed loop systems

A CGM can work with an insulin pump to form a hybrid closed loop system (also known as an artificial pancreas or automated insulin delivery). Using this helps to automate your type 1 treatment and reduce the number of decisions you need to make every day.

Our hybrid closed loop page has information about which CGMs, insulin pumps and programmes work together to make a hybrid closed loop system.

The manufacturers sites listed above will also tell you what technology each CGM is compatible with.

Smart pens

A CGM can work with a smart insulin pen, which is a type of insulin pen that records how much insulin you take and when. Connecting a smart pen with a CGM can help you record information on your glucose levels and the amount of insulin you’re taking, which can help you make decisions about your treatment.

What continuous glucose monitors are available?

These are the main manufacturers of CGMs. Visit their websites for more information:

GlucoRX  and Medtrum are also available but there is currently limited evidence of accuracy for people with type 1.

Can I change the colour of a continuous glucose sensor?

CGMs, as well as flash sensors, are usually white or a light grey. This can make them stand out, particularly if you have dark skin, and make some people feel self-conscious. Adhesive patches are available in a variety of skin tones, colours and patterns and you can search for them online.

Can I get a continuous glucose monitor on the NHS?

The NHS recommends CGM for everyone with type 1 diabetes in England and Wales. CGMs that work with insulin pumps to form a hybrid closed loop system are normally approved by your hospital-based Diabetes Healthcare Team. Alternatively, your GP can prescribe CGM, but most of the CGMs available on prescription don’t work as part of a hybrid closed loop system. Find out more about which CGMs work with which insulin pumps in hybrid closed loop systems.

Get more information on how you can access CGM on the NHS in England and Wales, Scotland and Northern Ireland.

How much does a continuous glucose monitor cost?

Most CGM sensors cost around £40 – £60 each. Unless you have a compatible mobile phone, there is also an initial cost for a handset/receiver. There are then ongoing running costs for sensors, transmitters, and adhesive covers. However, in England and Wales you should be able to get the CGM system you need on the NHS.

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Can I get a continuous glucose monitor on the NHS?

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Smart insulin pens

A smart insulin pen is a reusable self-injection pen, which records information about how much insulin you inject and the timing of it.

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Blood glucose meters

Blood glucose meters measure the amount of glucose in the blood. They are an important part of managing your blood glucose levels.

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Continuous glucose monitoring

Continuous glucose monitoring can help you manage your glucose levels in real-time and relieve the burden of having to do multiple finger prick tests throughout the day.

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Flash glucose monitoring

A flash glucose monitor is a small wearable device that you scan with a reader or mobile phone to check your glucose levels.

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Hybrid closed loop technology – also known as the artificial pancreas – automates many of the decisions that you have to make on a daily basis when you have type 1 diabetes.

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